Add Nitrogen to R2 Soybeans for a Big Yield Boost?

One great thing about soybeans – they make their own nitrogen. But is it enough? Maybe not, especially as farmers push for higher yields.

Pioneer conducted a small-plot nitrogen fertility experiment earlier in 2015, comparing nitrogen rates of 0, 25 and 50 lbs. per acre. The N was hand-applied as ammonium nitrate during the R2 growth stage.

The results? Adding 50 lbs. of N per acre at R2 helped pile on an additional 4.8 bu. per acre. Pioneer saw similar yield increases using two different varieties.

But University of Illinois Extension specialist Emerson Nafziger has said other experiments have proven inconsistent. One test did show a 6 bu. per acre gain, but he says there was no clear relationship seen between yields and midseason fertilizer use.

“These results provide no support for the idea that the higher the yield, the more response to fertilizer nitrogen,” he says. “In fact, yields above 70 bushels seemed more likely to show yield decreases from adding nitrogen, though these differences were small and not statistically significant.”

A few years back, University of Nebraska researchers compiled the results of 67 published studies and determined that positive responses to N fertilization only happened about half the time, with an average yield boost of 8 bu. per acre.

“N fertilization of soybeans still carries a financial risk even under high yielding environments,” he notes. “Local trials can help determine whether or not the practice makes sense in individual situations.”

Nafziger agrees and recommends creating on-farm strip trials to investigate the potential benefits across a wide range of fields and soils.

Pioneer recommends experimenting with lower rates (20-30 lbs. per acre) of N, and then test at higher rates if you observe a cost-effective yield increase.

Some years ago I did some on farm replicated tests comparing Chilean nitrate and their potash of soda against an untreated check. The potash of soda was statistically different to the tune of about 8 bu/acre.